Lasers and radar build a 3D Roman bridge

There’s no troll living under this Roman bridge, but it is hiding secrets all the same. This 3D model made using lasers and radar will help to expose them.

The Roman Segura bridge was built in the 2nd century AD under the emperor Trajan and straddles the river Erges, which forms the border between modern-day Spain and Portugal. Researchers at the University of Vigo, Spain, mapped it by scanning a laser beam across its surface and measuring the time it took for the light to return. Then radar probed beneath the bridge’s surface to reveal hidden structures without damaging it.

Under one of the bridge’s arches, for example, the team found decorative engravings cut during the Renaissance. Along with scans of 80 similar sites in Spain, the results offer a unique chance to peer into the region’s rich Roman past – and to preserve it for future generations.